since opinions differ as to whether the oxidative and glycolytic capabilities of skeletal muscle are altered in acute infection, the activities of two oxidative and one glycolytic enzyme were determined in homogenates of skeletal muscle of rats. groups were inoculated with francisella tularensis 72 h prior to study or with salmonella typhimurium or streptococcus pneumoniae 48 h before enzyme analysis, for comparison with noninfected controls. the activities of six lysosomal enzymes (acid hydrolases) and protein and dna concentrations were also measured. all determinations were made separately on red (slow twitch) and white (fast twitch) muscle tissue, because these muscle fiber types function during different types of exercise. in the tularemia- and salmonella-infected rats, the oxidative enzymes of muscle were decreased to 56 to 83 and the glycolytic enzyme to 30 to 75 of control activities. reductions during tularemia were statistically correlated with whole-cell protein degradation, while that of the glycolytic enzyme was paralleled by activation of lysosomal enzymes. in the pneumococcal infection, only reduced glycolytic activity was significant. muscle dna concentrations were unchanged in any infection